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1Back to top Go down   Main Bearings check Torque  Empty Main Bearings check Torque on Sun May 06, 2012 5:41 am

Lazyboy

Lazyboy
Silver member
Silver member
I was told by a BMW Technician yesterday that at 120,000km as routine maintenance I should check the torque on the Crank Main Bearings. Is this correct ????


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1984 BMW K100RT

Bikes Name: Lazyboy
    

2Back to top Go down   Main Bearings check Torque  Empty Re: Main Bearings check Torque on Sun May 06, 2012 5:55 am

charlie99

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i would suggest if your doing that (and its worth doing )....at least get some plasitgauge and check the gap of the main bearings as well

check the references and confirm that its still in spec .......

loose bearing caps and bottom ends have a decided affect on oil presure and longetivity of the whole deal ..

cheers


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cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OMain Bearings check Torque  Au-log10

'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..
    

3Back to top Go down   Main Bearings check Torque  Empty Main Bearings check Torque on Sun May 06, 2012 6:07 am

Lazyboy

Lazyboy
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Hi Charlie 99 Thanks for the promt reply. Does this also include the big end bearings ?


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1984 BMW K100RT

Bikes Name: Lazyboy
    

4Back to top Go down   Main Bearings check Torque  Empty Re: Main Bearings check Torque on Sun May 06, 2012 6:14 am

charlie99

charlie99
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if you have the side cover off ...why not ?

i think there is a download of "the workshop "manual available in the forum ....if you dont already have it ....or a good reference at least .

a word of caution though ....some manufacturers list the bolts and nuts as one use only ...i guess they suffer from "stretch " under torque conditions ....weird i know ...but i did notice it somewhere


__________________________________________________
cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OMain Bearings check Torque  Au-log10

'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..
    

5Back to top Go down   Main Bearings check Torque  Empty Re: Main Bearings check Torque on Sun May 06, 2012 6:29 am

Inge K.

Inge K.
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@charlie99 wrote: a word of caution though ....some manufacturers list the bolts and nuts as one use only ...i guess they suffer from "stretch " under torque conditions ....weird i know ...but i did notice it somewhere

Good tip, Charlie. Common in the big ends on any engine.
The bolts is designed to stretch, when they`re properly torqued.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

6Back to top Go down   Main Bearings check Torque  Empty Main Bearings check Torque on Sun May 06, 2012 6:55 am

Dennis

Dennis
Platinum member
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Hopefully I can add something on the technical side of re-tensioning the bolts. It isn't possible to just place a torque wrench on the bolts, set to the correct torque value and pull on the nut. This doesn't work because the "starting torque" is greater than the original torque setting the nut was pulled up to. The nut must be backed off first by some amount of a turn, maybe half a turn, then retensioned to the correct value. If you use ne big end bolts, they need to be tensioned either in stages, or by the initial tension then degrees of rottion method. FWIW, some high performance engine builders actually tension the bolts to around 80% of the final value, 3 times, completely releasing the nut each time, then final tension on the fourth time. This is done to match the threads to each other under load, which is said to prevent the nut bedding into the bolt under engine load, so reducing the big end bolt tension slightly. Hope this helps, Dennis.

    

7Back to top Go down   Main Bearings check Torque  Empty Re: Main Bearings check Torque on Sun May 06, 2012 7:14 am

charlie99

charlie99
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aye! dennis ....always good to read the recommended tecnique

there are manys recommended methods ...but always good to check with the manufacturers recomendatons ...they usually know the limits and design spec of the part they use .....but again there is some degree of unwanted confusion about what is safe...and marketing ....i read many times that "replacement with new parts "should be performed at every instance of proceedure "...but we all know that its "b/s" ...and it is quite safe to go again well for a few times at least ....not counting those oops events ...that many unfarmilliar to methods commonly make .. so the balence is ... "replace all parts, just in case " ..

i guess has to be a big plus to reliability ....but i call it "risk management" and it sucks if your a poor soul just trying to get the "beast" back together.


__________________________________________________
cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OMain Bearings check Torque  Au-log10

'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..
    

8Back to top Go down   Main Bearings check Torque  Empty Re: Main Bearings check Torque on Sun May 06, 2012 8:01 am

Inge K.

Inge K.
VIP
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@charlie99 wrote:i guess has to be a big plus to reliability ....but i call it "risk management" and it sucks if your a poor soul just trying to get the "beast" back together.
Poor or not.....a stretch bolt (identified by a smaller diameter at a small part of the length) is quite important to change everytime.

If you stretch it another time, you`re in the risk that it snap when in service..........
then you really get that poor feeling.



Last edited by Inge K. on Sun May 06, 2012 8:21 am; edited 1 time in total (Reason for editing : dyslexic moment.)


__________________________________________________
Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

9Back to top Go down   Main Bearings check Torque  Empty Re: Main Bearings check Torque on Sun May 06, 2012 10:25 am

charlie99

charlie99
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yes inge,,, for sure if it is stretched ..i was having a wimper at the "must do " mentality .... sall good mate


__________________________________________________
cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OMain Bearings check Torque  Au-log10

'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..
    

10Back to top Go down   Main Bearings check Torque  Empty Re: Main Bearings check Torque on Mon May 07, 2012 5:04 am

ReneZ

ReneZ
Life time member
Life time member
This is a difficult one, as we don't know how close the bolts used are to their mechanical maximum. I have seen a fair share of damages of larger diesel engines due to issues with the big end bolts. These are often hydraulically 'torqued', by stretching the bolts with a specified amount of hydraulic pressure using a hydraulic nut. Still some of them got loose/broke/etc and resulted in some hefty expensive damages (in more than 50% the engines were scrap). Checking other bolts at times proved them elongated ('overstretched'/plastic deformed) and/or with little cracks, mostly in the first few turns of the thread, with various extend of 'fatigue fractures'. The cyclic loading of these bolts can be very high, so renewing is a risk-minimising action, where the alternative (a substantial damage) is not an acceptable option.
The difficulty with our bikes is that we don't necessarily know who did what before; having the bolts oiled/greased before applying torque that is specified for a dry fit can already overtighten bolts, resulting in early fatigue and cracks/fractures.
Hope it makes a bit of sense. Basically going through the loosening and re-tightening of the old bolts could become an issue. For the cost I think its a risk you wouldn't want to take. However you mind or wallet might tell you different.


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Greetings from Florida! Having a 'new' K  :cyclops:    Surprised-o: 

Rene


BMW K100 - 1985 (0030029) Main Bearings check Torque  Rain
BMW K1200GT - 2003 (ZK01223)
    

11Back to top Go down   Main Bearings check Torque  Empty Re: Main Bearings check Torque on Mon May 07, 2012 8:45 pm

92KK 84WW Olaf

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I dont know how to take this one. I have a Clymer manual, there is nothing aboutt his in it.

I have regularly gone over 150k miles in cars and never heard of doing this. My K100 has almost 96k miles on it and I would be going on basis of leave well alone if its fine, which it is. I am no expert on these bolts but the bit I do know is that they stretch and so it would seem one would actualy have to replace the cap bolts. I think if I was going that far I would leave alone or else replace the shells as well. My own decision is not to do this item.


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1992 K100LT 0193214 Bertha Alaska Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 105,200 miles
1983 K100RS 0011171 Fricka 606 29,495 miles Damn K Pox Its a Bat outta Hell Now 36,188  miles
    

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